Skały oolitowe dolnego kambru północno-wschodniej części obniżenia podlaskiego

Abstract

OOLITIC ROCKS OF LOWER CAMBRIAN AGE IN THE NE PART OF THE PODLASIE DEPRESSIONSummaryIn the north-eastern part of the Podlasie depression the laminarite complex (the Bug Beds according to J. Znosko, 1965) is discordantly overlain with a biapartite series of the Lower Cambrian deposits, showing a marked sedimentary gap and a considerable stratigraphical hiatus.The rook complex of Lower Cambrian age is built, in its lower part, of the Suwałki sandstones, in its upper part, of the clay rocks of the Batlic Beds (J. Znosko 1965).In the upper clayey portion of the Baltic Beds of Lower Cambrian age a specifically developed series occurs consisting of ferruginous rocks that make a uniform and monotonous, naturally bipartite lithostratigraphical horizon (Fig. 2). In the lower part it consists of ferruginous oolitic siltstones, locally with a thin layer of fine-grained ferruginous sandstones at the bottom, in the upper part – of ferruginous oolitic rocks.Mineral and chemical composition (Tables 1, 2, 3) of the ferruginous rocks is monotonous and, as a rule, slightly differentiated. The rocks are built of ferruginous oolites, detrital quartz, cay minerals and carbonates – mainly calcite and siderite in small amounts. Chamosite, iron hydroxides and oxides, muscovite and occasionally fragments of feldspars and accessory pyrite appear subordinately. Among heavy minerals are found zircon and tourmaline. Content of total iron ranges in the rocks, considered from 16,0 to 43,0%. Thickness in the series of ferruginous rocks is regular and amounts, to 0,7-0,9 m. Position in the section, as well as character and development of the ferruginous rock allow us to relate their genesis to a rapidly initiated and suddenly terminated deposition, which violently although probably for a short moment only broke a slow and scarcely differentiated sedimentation of clays. The complex of lithofacial features of the rocks under consideration markedly points to the turbulent and heavy conditions of the ferruginous material precipitation.